Retinol (Vitamin A) is known to be necessary to the biochemistry of human vision. Through a series of reactions the retinol is converted through retinal isomers to rhodopsin ("visual purple"). Irradiation of the rhodopsin with visible light in turn causes a series of isomerization reactions through the retinal isomers to opsin resulting in excitation of the retinal rod cells and generation of a visual nerve impulse. A deficiency of Vitamin A in the system leads to reduced visual sensitivity (especially night blindness) and in extreme cases (e.g., keratomalacia or xerophthalmia) to complete blindness.
Vitamin A is also known to be necessary to the proper function of the epithelial tissues. Deficiency of Vitamin A in such cases results in disorders such as reduced resistance to infection through epithelial surfaces.
Increases in the level of Vitamin A in the body may to some extent be obtained by administering doses of Vitamin A directly to an individual. However, there is a limited bodily tolerance to Vitamin A, and overdoes of Vitamin A can lead to toxic effects. Since the tolerance level varies widely among individuals, it is not generally advisable to administer substantial doses of Vitamin A except under carefully controlled circumstances.
It is well known that carotene is the precursor of Vitamin A. (There are several carotene isomers, including the alpha-, beta- and gamma-carotene isomers. Of these the beta-carotene isomer has the most Vitamin A activity and is also the most common. As used herein, the term "carotene" is limited to B-Carotene. Carotene is oxidized by liver enzymes to produce Vitamin A. Significantly, however, the enzyme metabolism produces only the amount of Vitamin A that can be utilized by the body; it does not produce an overdose of Vitamin A. Consequently, an individual can be administered doses of carotene in quantities large enough to produce optimum levels of Vitamin A in the body without the risk cf a toxic Vitamin A reaction. Excess carotene which is administered is stored in fatty tissues and organs.
The carotenes, particularly beta-carotene, are present in many common foods, primarily the green and yellow vegetables such as tomatoes, citrus fruits, carrots, squash, turnips, broccoli and spinach. The concentration of carotene in these vegetables is relatively low, and a person must consume substantial quantities of the vegetables to have a high intake level of carotene. The normal diet for most people does not include such large quantities of these vegetables, so there has developed a commercial market for concentrated carotene dietary supplements, particularly those in which the carotene is beta-carotene because of its high Vitamin A activity. These supplements normally have been produced by extraction of carotene from vegetables such as carrots by use of petrochemical solvents. The resulting carotene, usually in crystalline form, can be expected to be associated with at least residual quantities of such solvents. This is particularly true when the carotene is administered in a dosage form in which it is dispersed in a petrochemical or other "synthetic" oil. The presence, even in minute amounts, of such petrochemical residues in the carotene supplements has caused apprehension among users of the supplements.
It is also known that certain algae, especially those in the classes Rhodophyta (red algae) and Chlorophyta (green algae), are good sources of carotene. The carotene content of species of the genus Dunaliella have been reported in U.S. Pat. Nos. 4,115,949 and 4,119,895 and in Acta Chem. Scand. 23, 7, 2544-2545 (1979). Similar data for the genus Chlorococcum has been disclosed in U.S. Pat. No. 2,949,700. In the past, however, all extraction processes to produce the carotene from algae have involved the use of petrochemical solvents, which results in the same contamination problems discussed above for the vegetable extractions. In addition, many of the algal extraction processes have involved drying of the alga, which has been found to degrade the carotene.
In addition to the use of carotene as a precursor for Vitamin A, there have recently been reports in the literature that suggest that carotene is itself useful in the prevention of certain types of cancers which are believed to be promoted by oxidizing free radicals. It is postulated that carotene, which has an affinity for such free radicals, may serve to reduce the free radical level in the body, thereby reducing the occurrence of free radical initiation of malignancies. There are studies currently underway which are expected to provide more information regarding the effects of carotene on such cancers.
It would therefore be of benefit to have carotene available in a form which would be safe and therapeutically useful for humans, and which would not have the disadvantages noted.
More particularly, it would be of benefit to have such carotene available in a stable form. B-carotene is extremely sensitive to oxidation. It is usually stored in tightly sealed containers. However, even with such precautionary measures, there is sufficient oxygen available to cause a substantial decrease in activity in about eight (8) days.
It is an object of the present invention to prepare relatively highly pure, clear and stable B-carotene.
We have found that this object is achieved by a process for the preparation of B-carotene which comprises reacting 2-10 parts of B-carotene, preferably in the presence of an antioxidant such as butylated hydroxytoluene with 98-90 parts of polysorbate.
As used herein, B-carotene has the chemical formula ##STR1## and polysorbate the chemical formula
The reaction between the B-carotene and the polysorbate is carried out in the following manner:
(1) The polysorbate (90-99 parts) is heated with an antioxidant, such as buylated hydroxytoluene (BHT), in order to remove any water. This is carried out under stirring at normal atmospheric to moderately increased pressures and at temperatures in the 100.degree. C. to 120.degree. C. range, or under vacuum at reduced temperatures. Removal of the water separated out is facilitated by bubbling dry argon or nitrogen through the polysorbate.
(2) Once the water is substantially completely removed, the B-carotene (1-10 parts) is added. Conditions are maintained until the B-carotene is dispersed in the solution. At this time the temperature is increased to about 160.degree.-180.degree. C. at atmospheric pressure. Once again, the inert atmosphere is maintained. Conditions are held constant for approximately 1-2 hours before the heat is removed;
(3) Immediately thereafter, there are added 2-5 parts t-butylhydroquinone (TBHQ) and 2-5 parts p-aminobenzoic acid (PABA), under an inert atmosphere. The stirring is continued as the solution is allowed to cool below 30.degree. C.
(4) The resulting deep orange syrupy solution is assayed for activity and subsequently packaged in dark containers.
Examples of particularly suitable polysorbates are: glyceryl polyoxyethylene glycol ricinoleate, glycerol polyoxyethylene glycol hydroxystearate, polyoxyethylene-20 sorbitan mono-oleate, polyoxyethylene-20 sorbitan monostearate, polyoxyethylene-sorbitan monolaurate, and the adduct monohydroxystearic acid with 15 units of ethylene oxide.
Examples of conventional antioxidants which can be used in the process according to the invention are butyl-hydroxytoluene, butylhydroxyanisole and d,1-.alpha.-tocopherol. The antioxidants are generally used in amounts of from 10 to 20% by weight, based on the B-carotene employed.
Despite the belief held by the skilled in the at, no isomerization of the B-carotene takes place at these temperatures. The stabilized B-carotene produced in accordance with the invention has the following chemical structure: ##STR2##
The following example is given in order to illustrate the invention, but is not to be construed in limitation thereof.